#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
    int a[4],i,s;
    for(i=0;i<4;i++)
    cin>>a[i];
    sort(a,4,0)
    s=a[1]*a[2]+a[3]*a[4];
    cout<<s;
    
    return 0;
}